Use mojo SystemTray interfaces for both mash and classic ash

ash/mus/window_manager_application.h

Index: ash/mus/window_manager_application.h
diff --git a/ash/mus/window_manager_application.h b/ash/mus/window_manager_application.h
index fee064479246edd4249fd420f8d1458204f48088..983c3a15ceb869178ad78cc9287b5bd73764369f 100644
--- a/ash/mus/window_manager_application.h
+++ b/ash/mus/window_manager_application.h
@@ -11,7 +11,6 @@
 #include <set>
 
 #include "ash/public/interfaces/shelf.mojom.h"
-#include "ash/public/interfaces/system_tray.mojom.h"
 #include "ash/public/interfaces/wallpaper.mojom.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
@@ -55,7 +54,6 @@ class WindowManager;
 class WindowManagerApplication
     : public shell::Service,
       public shell::InterfaceFactory<mojom::ShelfController>,
-      public shell::InterfaceFactory<mojom::SystemTray>,
       public shell::InterfaceFactory<mojom::WallpaperController>,
       public shell::InterfaceFactory<ui::mojom::AcceleratorRegistrar>,
       public mash::session::mojom::ScreenlockStateListener {
@@ -86,10 +84,6 @@ class WindowManagerApplication
   void Create(const shell::Identity& remote_identity,
               mojom::ShelfControllerRequest request) override;
 
-  // InterfaceFactory<mojom::SystemTray>:
-  void Create(const shell::Identity& remote_identity,
-              mojom::SystemTrayRequest request) override;
-
   // InterfaceFactory<mojom::WallpaperController>:
   void Create(const shell::Identity& remote_identity,
               mojom::WallpaperControllerRequest request) override;
@@ -114,7 +108,6 @@ class WindowManagerApplication
   scoped_refptr<base::SequencedWorkerPool> blocking_pool_;
 
   mojo::BindingSet<mojom::ShelfController> shelf_controller_bindings_;
-  mojo::BindingSet<mojom::SystemTray> system_tray_bindings_;
   mojo::BindingSet<mojom::WallpaperController> wallpaper_controller_bindings_;
 
   std::set<AcceleratorRegistrarImpl*> accelerator_registrars_;